__author__ = 'F3285189'
import tkinter as tk

class App(tk.Tk):
    def __init__(self,*args, **kwargs):
         tk.Tk.__init__(self, *args, **kwargs)
         self.label = tk.Label(self, text="", width=20, anchor="w")
         self.label.pack(side="top",fill="both",expand=True)
         self.print_label_slowly("Hello, world!")

    def print_label_slowly(self, message):
         '''Print a label one character at a time using the event loop'''
         t = self.label.cget("text")
         t += message[0]
         self.label.config(text=t)
         if len(message) > 1:
             self.after(500, self.print_label_slowly, message[1:])
app = App()
app.mainloop()